1. Field of the Invention
The present invention relates to photo-optical switching mechanisms and more particularly to photo-optical key switches wherein positive acting tactile feel is provided and wherein the switch structure is a modular assembly for demountable incorporation into a keyboard support.
2. Description of the Prior Art
One of the problems with prior art switches both electrical and as well as photo-optical has been the height and profile of the switch mechanism in relation to the surrounding mounting or supporting areas. The higher the key switch profile the more bulky in appearance is the keyboard utilizing the key switch. An additional undesireable feature of the prior art photo-optical switches is the off center location of the actuating spring mechanism against the stem and key of the switch. The off center action causes the switch key top to cock to one side due to the major spring pressure being directed against one side of the switch body.
In earlier style key switches of the photo-optical type the movable parts were not positively locked within the fixed part permitting the two subassemblies to become separated with relatively little effort. The effect of tactile feel, which is highly desireable in order for the operator to determine just when the switch has been "made" or closed is difficult to control and in the past has depended mainly on spring pressure or force. In the present design the tactile feel is positive and designed into the device as an element of a combination.
Prior art photo-optical switches which employ LED light generators and detector pairs utilized a light interrupting element which in the "up" position broke or interrupted the light beam while the "down" position the light beam was coupled through by means of the configured structure of the switch. However, in order to further lower the overall profile of the switch the key stem travel is lessened or shortened so that in the instant structure as claimed in the "up" position the beam is available and uninterrupted while in the "down" position the beam is interrupted or blocked.
The travel (vertical up and down movement of the key) is important for high speed data entry in that the operator cannot tell from touch-no tactile feedback-when or if the switch is closed or made and this effectively breaks the rhythm of the keyboard utilization and in addition creates errors in operation and general slowness in overall key switch actuation. One of the draw backs of the so called membrane keyboard is its lack of travel and uncertain tacticle feel.